Energy Procedia 50 ( 2014 ) 19 – 29

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ScienceDirect

1876-6102 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi: 10.1016/j.egypro.2014.06.003

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20 Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29

suggest the need of technological alternatives to assure their solution. One of these technological alternatives is generating electricity as near as possible of the consumption site, using the renewable energy sources, that do not cause environmental pollutions, such as wind, solar, tidal and hydro-electric power plants [2, 3]. Hydro-electric power is a form of renewable energy resource, which comes from the flowing water. To generate electricity, water must be in motion. When the water is falling by the force of gravity, its potential energy converts into kinetic energy. This kinetic energy of the flowing water turns blades or vanes in a hydraulic turbines, the form of energy is changed to mechanical energy. The turbine turns the generator rotor which then converts this mechanical energy into electrical energy and the system is called hydro-electric power station [4]. The first hydro-electric power systems were developed in the 1880's. According to the international energy agency (IEA), large-scale hydro-electric plants currently supply 16% of the world's electricity. However, such kind of projects requires tremendous amounts of land impoundment, dams and flood control, and often they produce environmental impacts [5]. Micro-hydro-electric power plants are one of an alternative source of energy generation. They are the smallest type of hydro-electric energy systems. They generate between (5) and (100) Kilowatt of power when they are installed across rivers and streams. - It acts much like a battery, storing power in the form of water. In particular, the advantages that micro-hydro-electric power plant has over the same size wind, wave and solar power plants are: - High efficiency (70-90%), by far the best of all energy technologies. - High capacity factors (> 50%) compared with 10% for solar and 30% for wind power plant. -Slow rate of change; the output power varies only gradually from day to day not from minute to minute. - The output power is maximum in winter. Comparative study between small-hydro-electric power plants (up to 10 MW capacity) and micro-hydro-electric power plants (up to 100 KW capacity) reveals that the former one is more capital intensive and involves major political decisions causing difficulties in different implementation phases. On the other hand micro-hydro-electric power plants are low cost, small sized and can be installed to serve a small community making its implementation more appropriate in the socio-political context. Many of these systems are " run-of-river" which does not require an impoundment. Instead, a fraction of the water stream is diverted through a pipe or channel to a small turbine that sits across the stream, as shown in figure (1). So, there is a scope for harnessing the micro-hydro-electric power plant potentiality by identifying proper site and designing appropriate power generation systems. Properly designed micro-hydro-electric power plant causes minimum environmental disruption to the river or stream and can coexist with the native ecology.

Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29 21

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22 Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29

To compute the cross-sectional area of a natural water course, it should be divided into a series of trapezoids. Measuring the trapezoid sides, marked rules, the cross-section would be given by:

(1)

Where a = width of top river (m) b = width of bottom river (m)

= average height of water in the river (m). ii- Measuring the velocity (Vr): Since the velocity both across the flow and vertically through it is not constant, it is necessary to measure the water velocity at a number of points to obtain a main value. The velocity can be measured by a floating object, which is located in the center of stream flow. The time (t) in seconds elapsed to traverse a certain length (L) in meter is recorded. The surface speed (m/s) is given as:

(2) To estimate the average flow speed (Vr), the above value must be multiplied by a correction factor, that may vary between (0.6) and (0.85), depending on the water course depth and their bottom and river bank roughness (0.75 is a well-accepted value).

(3) Then, the flow rate can be calculated as:

(4)

Where Q = water flow rate (discharge) of the river or stream.

2.3. Weir and open channel [4]

In case of low discharge rivers (less than 4 m3 /s), it may be possible to build a Weir. It is a low wall or dam across the stream to be gauged with a notch through which all the water may be channeled. A simple linear measurement of the difference in level between the up-stream water surface and the bottom of the notch is sufficient to quantify the flow rate (discharge). Several types of notch can be used such as rectangular, Vee or trapezoidal. The actual notch may be metal plate or hard wood with sharp edges, the flow rate through it can be given as [4]:

(5)

Where W = Weir width (m) h = Weir height (m) If w = 3h then the Weir dimensions can be calculated. The most important thing to consider while constructing the headrace open channel to make slope of channel only slightly elevated because higher slope can lead to higher velocity of water which can then cause erosion in the channel surface. In open channel foundation two requirements must be satisfied:

The stability: channel is a rigid structure and do not permit deformations Channel does not support thrust or up lift pressure. The flow of water in open channel is considered uniform

when: The water depth, area and velocity in every cross-section of the channel are constant. The energy gradient line, surface line and bottom channel line are parallel to each other.

Based on these concepts Manning found that [4]:

(6)

Where Q = flow rate of water in uniform open channel. nch = Manning factor. Sf = section factor . Sch = channel bottom line slope (hydraulic gradient) which normally is the bed slope.

Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29 23

(7)

Where open channel cross-sectional area. (8)

hydraulic radius of the section area. (9)

The open channel velocity (Vch) can be calculated as: (10)

2.4. Trash rack design [4] To prevent the trash from getting entry into the entrance flume, bars at certain spacing (called trash rack) are placed in a slanting position (at an angle 60 to 80 with horizontal). The maximum possible spacing between the bars is generally specific by the turbine manufacturers. Typical value are (20-30 mm) for Pelton turbines, (40-50 mm) for Francis turbines and (80- 100 mm) for Kaplan turbines. A screen or grill is always nearly at the entrance of both pressure pipes and intakes to avoid the entrance of floating debris. The flow of water through the rack also gives rise to a head loss. The trash rack coefficient (Ktr) depends on the bar shape and may be vary from (0.8) to (2.4). 2.5. Penstock design Penstocks (pipes) are used to conveying water from the intake to the power house. They can be installed over or under the ground, depending on factors such as the nature of the ground itself, the penstock materials, the ambient temperature and the environmental requirements. The internal penstock diameter (Dp) can be estimated from the flow rate, pipe length and gross head as [4]:

(11)

Where np = Manning's coefficient . Q = water flow rate (m3/s). Lp = penstock length in (m). Hg = gross head in (m). The wall thickness of the penstock depends on the pipe materials, its tensile strength, pipe diameter and the operating pressure. The minimum wall thickness is recommended as:

(12)

Where Dp = penstock diameter in (mm). tp = minimum penstock thickness in (mm). The pipe should be rigid enough to be handled without danger of deformation in the field. 2.6. Head measurement [4] The gross head (Hg) is the vertical distance between the water surface level at the intake and at the tailrace for the reaction turbines (such as Francis and Kaplan turbines) and the nozzle level for the impulse turbines (such as Pelton, Turgo and Cross-flow turbines). The modern electronic digital levels provide an automatic display of height and distance with about (4) seconds with measurement accuracy of (0.4 mm). Surveying by Global Positioning Systems (GPS) is already practiced and handheld GPS receiver is ideal for field positioning and rough mapping. Once the gross head is known, the net head (Hn) can be computed by simply subtracting the losses along its path, such as open channel loss, trash rack loss,

24 Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29

intake or inlet to penstock loss, gate or valve loss and penstock friction loss. 2.7. Turbine power [5] All hydro-electric generation depends on falling water. Stream flow is the fuel of a hydro-power plant and without it generation ceases. Regardless of the water path through an open channel or penstock, the power generated in a turbine (lost from water potential energy) is given as [4, 5]:

(13)

Where Pt = power in watt generated in the turbine shaft.

Q = water flow rate (m3/s). g = gravity acceleration constant (9.8 m/s2).

t = turbine efficiency (normally 80-90%). The turbine efficiency ( t) is defined as the ratio of power supplied by the turbine (mechanical power transmitted by the turbine shaft) to the absorbed power (hydraulic power equivalent to the measured discharge under the net head). It is noted that for impulse turbines, the head is measured at the point of impact of the jet, which is always above the down-stream water level. This amounts to reduction of the head. The difference is not negligible for low head schemes, when comparing the performance of impulse turbines with those of reaction turbines that use the entire available head. To estimate the overall efficiency of the micro-hydro-power plant, the turbine efficiency must be multiplied by the efficiencies of the speed increaser (if any) and the alternator. 2.8. Turbine speed [4] To ensure the control of the turbine speed by regulating the water flow rate, a certain inertia of rotating components is required. Addition inertia can be provided by a flywheel on the turbine or generator shaft. When the load is disconnected, the power excess accelerates the flywheel, later, when the load is reconnected, deceleration of the addition inertia supplies additional power that helps to minimize speed variation. The basic equation of the rotating system is:

(14)

Where w = turbine speed in (rad./sec.). Pt = turbine power (watt). Pl = load power (watt). B = turbine and generator friction torque coefficient (N.m/(rad./sec.)). J = moment of inertia of the whole rotating system (Kg/m2). When Pt = Pl +B * w2, dw/dt = 0 and w = constant. So operation is steady. When Pt is greater or smaller than (Pl +B * w2), the speed is not constant and the governor must intervene so that the turbine output power matches the generator output power. The motion equation of the whole system is a first-order differential equation and it can be solved numerically by Matlab software or Matlab Simulink or closed form solution. Then the turbine speed in r.p.m. can be determined as:

(15)

Any turbine, with identical geometric proportions, even if the sizes are different, will have the same specific speed (Ns). The specific speed is defined as [4]:

(16)

Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29 25

Where N = turbine speed in (r.p.m) which can be calculated from the solution of motional equation. Hn = net head in (meter). Pt = turbine power in (Kw). The specific speed constitute a reliable criterion for the selection of turbine type and dimension. After determination of turbine speed (N), the gear box ratio and the generator type can be selected. 2.9. Turbine selection [4, 6] Once the turbine power, specific speed and net head are known, the turbine type, the turbine fundamental dimensions and the height or elevation above the tailrace water surface that the turbine should be installed to avoid cavitation phenomenon, can be calculated. In case of Kaplan or Francis turbine type, the head loss due to cavitation, the net head and the turbine power must be recalculated. In general, the Pelton turbines cover the high pressure domain down to (50 m) for micro-hydro. The Francis types of turbine cover the largest range of head below the Pelton turbine domain with some over-lapping and down to (10 m) head for micro-hydro. The lowest domain of head below (10 m) is covered by Kaplan type of turbine with fixed or movable blades. For low heads and up to (50 m), also the cross-flow impulse turbine can be used. Once the turbine type is known, the fundamental dimensions of the turbine can be estimated as [6]: 2.9.1 For Pelton turbine If the runner speed (N), the net head and water flow rate (Q) are known, the dimensions of the Pelton turbine can be estimated from the following equations [6]:

diameter of circle describing the buckets center line in meters. (17)

bucket width in meters. (18)

Where K = number of nozzles.

nozzle diameter in meters. (19)

jet diameter in meters. (20)

jet velocity (m/s). (21)

The ratio D1/B2 must be always greater than (2.7). if this is not the case, then a new calculations with more nozzles number has to be carried out. If the turbine is Turgo at the same power of Pelton, the specific speed is double of that Pelton and the diameter is halved. 2.9.2 For Francis turbine It covers a wide range of specific speed, going from (50) to (350) corresponding to high head and low head respectively. The main dimensions can be estimated as [6]:

exit diameter in meters (22)

inlet runner diameter in meters (23)

inlet diameter in meters (24)

If Ns 163 then D1 = D2 2.9.3 For Kaplan turbine

26 Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29

the runner exit (outer) diameter in meters (25)

the runner hub (inlet) diameter in metersb (26)

2.9.4 For cross-flow turbine

runner diameter in meters (27)

runner length in meters (28)

jet thickness or nozzle width in meters (29)

3. Results

The design procedure of micro-hydro-electric power plant was implemented by Matlab Simulink computer program. After introducing the site measurements and calculations as input data to the computer program, the weir dimensions, open channel dimensions, penstock dimensions, turbine type, turbine size, turbine power, turbine speed, turbine efficiency, generator specifications and gear box ratio were determined. Figures (2,3) show the relation between turbine power and speed with gross head at different values of water flow rate. Figures (4,5) show the variation of turbine power and speed with water flow rate at different values of site head. From these results, the turbine power and speed were directly proportional with the gross head, but there were specific points for maximum power and maximum speed in case of water flow variation. Figures (6,7) show the variation of head loss with the gross head and water flow rate. It can be shown that the head loss was increased very high with increasing the water flow rate than that with increasing the gross head.

Fig. 2. Variation of turbine power with gross head at different values of water flow rate.

0 20 40 60 80 100 1200

100

200

300

400

500

600

700

800

Gross head Hg (m)

Turb

ine

pow

er

Pt

(KW

)

Q=1m3/s

Q=0.8m3/s

Q=0.6m3/s

Q=0.4m3/s

Q=0.2m3/s

Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29 27

Fig. 3. Variation of turbine speed with gross head at different values of water flow rate.

Fig. 4. Variation of turbine power with water flow rate at different values of gross head.

Fig. 5. Variation of turbine speed with water flow rate at different values of gross head.

0 20 40 60 80 100 1200

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Gross head Hg (m)

Turb

ine

spee

d

N (r

.p.m

)

Q=1m3/s

Q=0.8m3/s

Q=0.6m3/s

Q=0.4m3/s

Q=0.2m3/s

0 2 4 6 8 10 120

50

100

150

200

250

300

Water flow rate Q(m 3/s)

Turb

ine

pow

er

P

t(K

W)

Hg =10 m

Hg =8 m

Hg =6 m

Hg =4 m

Hg =2 m

0 2 4 6 8 10 120

500

1000

1500

2000

2500

3000

Turb

ine

spee

d

N

(r.p

.m)

Water flow rate Q(m 3/s)

Hg =10 m

Hg =8 m

Hg =6 m

Hg =4 m

Hg =2 m

28 Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29

Fig. 6. Variation of gross head with head loss at different values of water flow rate.

Fig. 7. Variation of water flow rate with head loss at different values of gross head.

4. Conclusions

i- Micro-hydro power continues to grow around the world, it is important to show the public how feasible micro-hydro systems actually are in a suitable site. The only requirements for micro-hydro power are water sources, turbines, generators, proper design and installation, which not only helps each individual person but also helps the world and environment as a whole. ii- The choice of turbine will depend mainly on the pressure head available and the water flow rate. There are two basic modes of operation for hydro power turbines: Impulse and reaction. Impulse turbines are driven by a jet of water and they are suitable for high heads and low flow rates. Reaction turbines run filled with water and use both angular and linear momentum of the flowing water to run the rotor and they are used for medium and low heads and high flow rate. iii- Regulated turbines can move their inlet guide vanes or runner blades in order to increase or reduce the amount of flow they draw. Cross-flow turbines are considered best for micro-hydro projects with a head of (5) meters or less and water flow rate (1.0) m3/s or less. iv- Micro-hydro power installations are usually run-of-river systems, which do not require a dam, and are installed on the water flow available on a year round basis. An intake structure with trash rack channels water via a pipe

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

2

4

6

8

10

12

14

16

Head loss Hl (m)

Gro

ss h

ead

Hg

(m)

Q =0.2 m3/s Q =0.6 m3/s Q =0.8 m3/s Q =1 m3/sQ =0.4m3/s

0 2 4 6 8 10 120

2

4

6

8

10

12

Head loss Hl (m)

Wat

er fl

ow ra

te

Hg=2m

Hg=4m

Hg=6m

Hg=8m

Hg=10m

Q(m3/s)

Bilal Abdullah Nasir / Energy Procedia 50 ( 2014 ) 19 – 29 29

(Penstock) or conduit down to a turbine before the water released down- stream. In a high head (greater than 50 m) and low water flow (less than 0.5 m3/s), the turbine is typically Pelton type connected directly to a generator with control valve to regulate the flow of water and turbine speed. References

[1] Mohibullah, M. A. R. and MohdIqbal Abdul Hakim: "Basic design aspects of micro-hydro-power plant and its potential development in Malaysia", National Power and Energy Conference (PECon) Proceedings, Kuala Lumpur, Malaysia, 2004.

[2] http:// www.microhydropower.net/ [3] http:// www.alternative-energy.info/micro-hydro-power-pros-and-cons/ [4] CelsoPenche: "Layman's guidebook on how to develop a small hydro site", Published by the European Small

Hydropower Association (ESHA), Second edition, Belgium, June, 1998. [5] Dilip Singh: "Micro-hydro-power", Resource Assessment Handbook, An Initiative of the Asian and Pacific

Center for Transfer of Technology, September, 2009. [6] European Small Hydropower Association (ESHA): "Energy recovery in existing infrastructures with small

hydropower plants", Sixth Framework Programme, Publication by Mhylab, Switzerland, June, 2010.